Post-CMP Cleaning and Apparatus

ABSTRACT

A method includes performing a first post Chemical Mechanical Polish (CMP) cleaning on a wafer using a first brush. The first brush rotates to clean the wafer. The method further includes performing a second post-CMP cleaning on the wafer using a second brush. The second brush rotates to clean the wafer. The first post-CMP cleaning and the second post-CMP cleaning are performed simultaneously.

BACKGROUND

Chemical mechanical Polish (CMP) processes are widely used in thefabrication of integrated circuits. When an integrated circuit is builtup layer by layer on the surface of a semiconductor wafer, CMP processesare used to planarize the topmost layer to provide a planar surface forsubsequent fabrication steps. CMP processes are carried out polishingthe wafer surface against a polish pad. A slurry containing bothabrasive particles and reactive chemicals is applied to the polish pad.The relative movement of the polish pad and wafer surface coupled withthe reactive chemicals in the slurry allows the CMP process to planarizethe wafer surface by means of both physical and chemical forces.

CMP processes can be used for the fabrication of various components ofan integrated circuit. For example, CMP processes may be used toplanarize inter-level dielectric layers and inter-metal dielectriclayers. CMP processed are also commonly used in the formation of thecopper lines that interconnect the components of integrated circuits.

After a CMP process, the surface of the wafer, on which the CMP processhas been performed, is cleaned to remove residues. The residues mayinclude organic matters and particles. In recent generations ofintegrated circuits, the sizes of the integrated circuit devices arereduced to a very small scale. This posts a demanding requirement to thepost-CMP cleaning than for older generations of integrated circuits. Forexample, the sizes of the metal particles that remain after the post-CMPcleaning cannot exceed a half of the critical dimension (the gatelength) of the transistors on the wafer. Obviously, with the reductionof the sizes of the integrated circuit devices, such requirement istightened.

In conventional post-CMP cleaning, brushes were used to remove theresidues on the wafers.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates Chemical Mechanical Polish (CMP) process inaccordance with some embodiments.

FIG. 2A illustrates a top view of a post-CMP cleaning process and aportion of a post-CMP cleaning apparatus in accordance with someembodiments, wherein four brushes are used.

FIG. 2B illustrates a top view of a post-CMP cleaning process and aportion of a post-CMP cleaning apparatus in accordance with someembodiments, wherein one of the brushes has an end aligned to a centerof the wafer.

FIG. 3 illustrates a cross-sectional view of a post-CMP cleaning processand a portion of a post-CMP cleaning apparatus in accordance with someembodiments.

FIG. 4 illustrates a top view of a post-CMP cleaning process and aportion of a post-CMP cleaning apparatus in accordance with someembodiments, wherein two brushes are perpendicular to other two brushes.

FIG. 5 illustrates a top view of a post-CMP cleaning process and aportion of a post-CMP cleaning apparatus in accordance with someembodiments, wherein two brushes are used.

FIG. 6 illustrates a top view of a post-CMP cleaning process and aportion of a post-CMP cleaning apparatus in accordance with someembodiments, wherein a single brush is used.

FIG. 7 illustrates a top view of a post-CMP cleaning process and aportion of a post-CMP cleaning apparatus in accordance with someembodiments, wherein a long brush swings during the cleaning.

FIG. 8 illustrates a top view of a post-CMP cleaning process and aportion of a post-CMP cleaning apparatus in accordance with someembodiments, wherein a pencil-type brush is used.

FIG. 9 illustrates a top view of a brush and a wafer, wherein thecontact area between the brush and the wafer has a contact width.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “underlying,” “below,”“lower,” “overlying,” “upper” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

An apparatus for performing post Chemical Mechanical Polish (CMP)cleaning and the post-CMP cleaning process are provided in accordancewith various exemplary embodiments. Some variations of some embodimentsare discussed. Throughout the various views and illustrativeembodiments, like reference numbers are used to designate like elements.

FIG. 1 schematically illustrates the CMP of a wafer in accordance withsome embodiments of the present disclosure. CMP system 10 includespolishing platen 12, polishing pad 14 over polishing platen 12, andpolishing head 16 over polishing pad 14. Slurry dispenser 20 has anoutlet directly over polishing pad 14 in order to dispense slurry ontopolishing pad 14.

During the CMP, slurry 22 is dispensed by slurry dispenser 20 ontopolishing pad 14. Slurry 22 includes a reactive chemical(s) that reactwith the surface layer of wafer 18. Furthermore, slurry 22 includesabrasive particles for mechanically polishing wafer 18.

Polishing pad 14 is formed of a material that is hard enough to allowthe abrasive particles in the slurry to mechanically polish the wafer,which is under polishing head 16. On the other hand, polishing pad 14 isalso soft enough so that it does not substantially scratch the wafer.During the CMP process, polishing platen 12 is rotated by a mechanism(not shown), and hence polishing pad 14 fixed thereon is also rotatedalong with polishing platen 12. The mechanism (such as a motor and/or agear) for rotating polishing pad 14 is not illustrated.

During the CMP process, polishing head 16 is also rotated, and hencecausing the rotation of wafer 18 fixed onto polishing head 16. Inaccordance with some embodiments of the present disclosure, polishinghead 16 and polishing pad 14 rotate in the same direction (clockwise orcounter-clockwise). In accordance with alternative embodiments, as shownin FIG. 1, polishing head 16 and polishing pad 14 rotate in oppositedirections. The mechanism for rotating polishing head 16 is notillustrated. With the rotation of polishing pad 14 and polishing head16, slurry 22 flows between wafer 18 and polishing pad 14. Through thechemical reaction between the reactive chemical in the slurry and thesurface layer of wafer 18, and further through the mechanical polishing,the surface layer of wafer 18 is planarized.

After the CMP, wafer 18 is cleaned through a post-CMP cleaning step. Thepost-CMP cleaning step may include a plurality of steps including andnot limited to, cleaning using an acidic chemical solution, cleaningusing an alkaline chemical solution, cleaning using a neutral chemicalsolution, and rinsing with De-ionized water (DI water). The post-CMPcleaning may also include a plurality of cycles, each including achemical solution cleaning step and a rinsing step.

FIG. 2 illustrates a top view of a stage in the post-CMP cleaning andthe respective cleaning apparatus 30 in accordance with someembodiments. Wafer 18, which has been undertaken the CMP process, hasresidues left on the surface of wafer 18, and the residues need to beremoved from wafer 18. The residues may include organic matters andparticles. The cleaning process is referred to as post-CMP cleaningprocess.

The cleaning apparatus 30 includes a plurality of brushes (alsosometimes referred to as brush rollers due to their circularcross-sectional shapes) 32 (including 32A, 32B, 32C, and 32D). Brushes32A, 32B, 32C, and 32D may be formed of Polyvinyl Alcohol (PVA) inaccordance with some embodiments of the present disclosure, or may beformed of other materials. Furthermore, Brushes 32A, 32B, 32C, and 32Dmay be made to have the form of sponges. During the post-CMP cleaningprocess, wafer 18 is rotated, for example, as illustrated by arrow 34.In the meantime, brushes 32A, 32B, 32C, and 32D also rotate withrespective to their own axes. The axes of brushes 32A, 32B, 32C, and 32Dare in the lengthwise directions of the respective brushes, and areparallel to the surface of wafer 18. Brushes 32A, 32B, 32C, and 32D havea cylindrical shape. Also, when viewed from right as shown in FIG. 2,the cross-sectional view of each of brushes 32A, 32B, 32C, and 32D iscircular, as shown in FIG. 9 (marked as 32 in FIG. 9), and hence whenthe brushes rotate, residues are removed from the surface of wafer 18.In accordance with these embodiments, the length of each of brushes 32Amay be smaller than diameter DIA of wafer 18, and may be equal to,greater than, or smaller than, radius DIA/2 of wafer 18.

Each of brushes 32A, 32B, 32C, and 32D is fitted to an end portion of arespective connecting component 40, which is configured to support therespective brushes 32A, 32B, 32C, and 32D. When connecting component 40is rotated, brushes 32A, 32B, 32C, and 32D are also rotated. Inaccordance with some embodiments, connecting component 40 is hollow witha space therein, and DI water and/or chemical solutions may be passedthrough the space into brushes 32A, 32B, 32C, and 32D, and dispensedonto brushes 32A, 32B, 32C, and 32D. In addition, each of brushes 32A,32B, 32C, and 32D is connected to one of driving components 42, which isconfigured to rotate and/or move/swing the respective connectingcomponent 40 and the respective brush. Accordingly, with the operationof the driving mechanism 42, brushes 32A, 32B, 32C, and 32D may berotated and/or swung, as will be discussed in detail in subsequentdiscussion. The driving components 42 may include, for example, motors,gliding guides, robot arms, gears (not shown), and the like.

During the cleaning, chemical solution (referred to as cleaning solutionhereinafter) 35 is sprayed onto the surface of wafer 18. Cleaningsolution 35 may include various types, and different types of cleaningsolution 35 may be used to clean different residues on wafers. Inaccordance with some embodiments, cleaning solution 35 includes an acidchemical solution, which may include an organic acid such as citricacid, an inorganic acid such as HNO₃, or the like. In accordance withsome embodiments, cleaning solution 35 includes an alkaline chemicalsolution, which may include an organic base such as NR₃ (with R beingalkyl), an inorganic base such as NH₄OH, or the like. Surfactants suchas sodium dodecyl sulfate may be added into cleaning solution 35 toreduce the surface tension of cleaning solution 35. Cleaning solution 35may include water as a solvent. Cleaning solution 35 may also useorganic solvents such as methanol. Cleaning solution 35 may also be anaqueous solution including peroxide. For example, cleaning solution 35may include H₂O₂ in water. With the rotation of wafer 18, cleaningsolution 35 is rolled into brushes 32A, 32B, 32C, and 32D, which usecleaning solution 35 to clean the surface of wafer 18 when they rotate.

In accordance with some embodiments of the present disclosure, thelocations of brushes 32A, 32B, 32C, and 32D are fixed, although brushes32A, 32B, 32C, and 32D also roll by themselves. The lengthwise directionof brush 32A may be aligned to a diameter 36 of wafer 18. Furthermore,brush 32A is disposed on the left side of wafer center 18A. The rightedge of brush 32A is also on the left side of wafer center 18A, and isspaced apart from wafer center 18A of wafer 18 by distance D1. Inaccordance with some exemplary embodiments, distance D1 is equal to ahalf of the contact width between brush 32A and wafer 18. For example,FIG. 9 illustrates a cross-sectional view of a portion of the structureshown in FIG. 2, wherein the cross-sectional view is obtained from theplane crossing line 9-9 in FIG. 2. As shown in FIG. 9, brush 32 contactswafer 18 and have a contact area, and the contact area has width W1. Inaccordance with some embodiments, distance D1 is equal to W1/2. Inaccordance with alternative embodiments of the present disclosure,distance D1 is greater than or smaller than W1/2.

Referring to FIG. 2 again, brush 32B may also be disposed on wafer 18.The lengthwise direction of brush 32B may also be aligned to diameter 36of wafer 18. Furthermore, brush 32B is disposed on the right side ofwafer 18, and hence is spaced apart from brush 32A. The left edge ofbrush 32B is on the right side of wafer center 18A, and is spaced apartfrom wafer center 18A by distance D2. In accordance with some exemplaryembodiments, distance D2 is equal to W1/2, wherein W1 is the contactwidth between brush 32B and wafer 18, as shown in FIG. 9. Distance D2may also be equal to, greater than, or smaller than distance D1. Also,distance D2 may be greater than or smaller than W1/2.

Brush 32A may cover all the way to the left edge 18B of wafer 18 inaccordance with some embodiments, and may extend slightly beyond (towardleft) left edge 18B of wafer 18. It is noted that since wafer 18 isbeing rotated, when the “upper edge,” “bottom edge,” “left edge,” and“right edge,” are referred to throughout the description, these termrefer to the geographical locations on wafer 18 at a time wafer 18 isviewed, rather than the fixed points that rotate with wafer 18. With therotation of both wafer 18 and brush 32A, brush 32A is able to brush allof wafer 18 except center region 18CR, with the center region 18CRhaving a radius equal to distance D1. In accordance with someembodiments, the left edge of brush 32A is on the right side of leftedge 18B. Accordingly, the length of brush 32A is smaller than theradius DIA/2 of wafer 18 in accordance with some embodiments.

Similarly, brush 32B may cover all the way to the right edge 18C ofwafer 18, and may extend slightly beyond (toward right) the right edge18C of wafer 18. Accordingly, with the rotation of both wafer 18 andbrush 32B, brush 32B is able to brush all of wafer 18 except centerregion 18CR, with the center region having a radius equal to distanceD2. In accordance with some embodiments, the right edge of brush 32B ison the left side of right edge 18C. Accordingly, the length of brush 32Bis smaller than the radius DIA/2 of wafer 18.

In accordance with some embodiments, as shown in FIG. 2B, brush 32A hasthe right edge spaced apart from center 18A by distance D1, which may beequal to, smaller than, or greater than, a half of the contact width(W1/2, FIG. 9). On the other hand, the left edge of brush 32B extends tobe aligned with wafer center 18A. Accordingly, brush 32B is able toclean substantially the entirety of wafer 18.

In conventional post-CMP processes, a single long brush was used, whichextends from one edge to the opposite edge of the wafer that ispolished. Accordingly, when wafer 18 is rotated, the edge portions ofwafer 18 are cleaned when they rotate directly underlying and in contactwith the respective brush, and not cleaned when they rotate away fromthe brush. However, the wafer has a center portion that has the diameterequal to the contact width (as shown in FIG. 9). The center portion isalways in contact with the brush regardless of which edge portions ofthe wafer are being brushed, and is always brushed. This may cause thecenter portion of the wafer to be over-brushed. The center portion maybe damaged or degraded due to the longer duration the sheer forceapplied to the center portion than to the edge portions. In addition,since water may be used, either in the cleaning solution or in the formof DI water, and water has a low electrical conductivity, charges maybuild up in some parts of the wafer due to longer contacting of thebrush to these regions, causing the corrosion of these portionsincluding the center portion of the wafer.

In the embodiments of the present disclosure, by using two brushes, withat least one, and possibly both brushes not extending to the centerregion 18CR of wafer 18, the damage/corrosion caused by theover-abrasion of brushes to the wafer is reduced. For example, in theembodiments shown in FIG. 2B, the brushing to the center region of wafer18 is reduced by a half. In the embodiments in FIG. 2A, the centerregion of wafer 18 is not brushed and cleaned. Instead, the centerregion 18CR is cleaned in another cleaning process, which may beperformed using a pencil-type brush.

In accordance with some embodiments of the present disclosure, brush 32Cis further disposed on wafer 18, and is used to clean wafer 18. Brush32C has a lengthwise direction parallel to the lengthwise direction ofbrushes 32A and 32B, and hence the lengthwise direction of brush 32C isparallel to diameter 36. Brush 32C is misaligned from diameter 36, towhich brushes 32A and 32B are aligned. The center of brush 32C may bealigned to a point that is between center 18A and the upper edge 18D ofwafer 18.

In accordance with some embodiments of the present disclosure, brush 32Dis disposed on wafer 18, and is used to clean wafer 18 also. Brush 32Dalso has a lengthwise direction parallel to the lengthwise direction ofbrushes 32A and 32B, and the lengthwise direction is parallel todiameter 36. Brush 32D is misaligned from diameter 36E, to which brushes32A and 32B are aligned. The center of brush 32C may be aligned to apoint that is between center 18A and the lower edge 18E of wafer 18.

Brushes 32C and 32D may have the same lengths or may have differentlengths. In addition, the distance from brush 32C to wafer center 18Amay be equal to or different from the distance from brush 32D to wafercenter 18A.

The damage/corrosion of wafers during the cleaning processes includecenter mode, middle mode, and edge mode, which correspond to thedamage/corrosion of the center region, middle region, and edge region ofthe wafers. By adjusting the lengths and the locations of brushes 32A,32B, 32C, and 32D, the brushing to wafer 18 may be more uniform, and theportions of the wafer that suffer from the damage/corrosion may bebrushed less, so that the damage/corrosion is reduced withoutsacrificing the quality of the cleaning process.

Referring back to FIG. 2A again, in accordance with some embodiments ofthe present disclosure, each of brushes 32A, 32B, 32C, and 32D may beconfigured to swing (or may be fixed in location) when rotates. Thedouble headed arrows 44 (also include 44A and 44B) schematicallyillustrate the swing direction and the swing range of the brushes. Forexample, brush 32A may swing left and right, as shown in by arrow 44B.The rightmost boundary of the swing range is wafer center 18A. When theright edge of brush 32A reaches wafer center 18A, brush 32A starts swingback to left until it reaches it left end of the swing range. The rightboundary of the swing range may also be any point to the left of wafercenter 18A. Brush 32A may start swinging back to right when the rightedge of brush 32A has distance D1 equal to a half of the contact widthW1 (FIG. 9), or when distance D1 is greater than or smaller than W1/2.

Brush 32A may also swing up (or down), as shown by arrow 44A. It isnoted when the terms “up” and “down” are used, these terms refer to thepositions found in the top view of wafer 18. If viewed in across-sectional view of wafer 18, when brushes swing “up” or “down,”they are still at the same level, and the contact area between thebrushes and wafer 18 remain unchanged. In accordance with someembodiments of the present disclosure, a first end of the swing range isas shown in FIG. 2A, wherein the center axis of brush 32A is aligned todiameter 36. The extending direction of the center axis of brush 32A isalso its lengthwise direction. At this position, brush 32A has a firstcontact area with wafer 18. The swing range may be equal to or greaterthan contact width W1 (FIG. 9). Accordingly, when brush 32A reaches thesecond end of the swing range, brush 32A and wafer 18 have a secondcontact area, which does not overlap the first contact area.

Similar to brush 32A, brush 32B may swing left and right, and/or up anddown, as shown by arrows 44A and 44B. Similarly, brush 32B may swingtoward left until its left edge reaches wafer center 18A, at which timebrush 32B will start swinging back to right. Brush 32B may also swingtoward left, and then swing toward right before its left edge reacheswafer center 18A. Also, brush 32B may swing up and down similar to brush32A. Brushes 32A and 32B may swing in a synchronized mode, for example,simultaneously swing to the right, and then simultaneously swing to theleft; or simultaneously swing upwardly, and then simultaneously swingdownwardly.

Brushes 32C and 32D may also swing up and down to compensate for thenon-uniformity in the brushing of different areas of wafer 18. Theoptimal locations and swing ranges of brushes 32A, 32B, 32C, and 32D maybe determined by inspecting the previously cleaned wafers, and adjustingthe locations and the swing ranges accordingly, so that over-brushedregions are brushed less, and under-brushed regions are brushed more.

FIG. 3 illustrates a cross-sectional view of the structure in FIG. 2,wherein the cross-sectional view is obtained in the plane containingdiameter 36. Wafer 18 is placed on and secured by chuck 45, which isrotated, and hence the overlying wafer 18 is rotated also. In accordancewith some exemplary embodiments of the present disclosure, drivingcomponent 42 includes gliding guide 46, to which connecting components40 are attached. By driving connecting component 40 to glide alonggliding guide 46, brushes 32A and 32B may swing back and forth. Inaccordance with alternative embodiments, the swing of brushes may beachieved use other mechanisms such as robot arms.

FIG. 4 illustrates the apparatus and the cleaning process in accordancewith some embodiments. These embodiments are similar to the embodimentsshown in FIG. 2A, except brushes 32B and 32C have their lengthwisedirections perpendicular to the lengthwise direction of brushes 32A and32B. By applying brushes 32B and 32C, the throughput of the post-CMPcleaning is increased. Again, each of brushed 32C and 32D may be swungin the directions represented by arrows 44C and/or 44D.

FIG. 5 illustrates the apparatus and the post-CMP cleaning process inaccordance with some embodiments. These embodiments are similar to theembodiments shown in FIG. 2A, except brushes 32C and 32D in FIG. 2A arenot used. The structure and operation of brushes 32A and 32B may beessentially the same as described for brushes 32A and 32B in FIG. 2A,and hence are not repeated herein.

FIG. 6 illustrates the apparatus and the post-CMP cleaning process inaccordance with some embodiments. These embodiments are similar to theembodiments shown in FIG. 2A, except brushes 32B, 32C, and 32D in FIG.2A are not used, and a single brush 32A is used. The structure andoperation of brush 32A may be essentially the same as described forbrush 32A in FIG. 2A, and hence are not repeated herein.

FIG. 7 illustrates the apparatus and the post-CMP cleaning process inaccordance with some embodiments. In these embodiments, brush 32E has alength equal to or greater than diameter DIA of wafer 18. Accordingly,at any given time, the brushed region crosses the entire diameter ofwafer 18. Brush 32E is configured to swing up and down, as shown bydouble headed arrow 44, so that the center region is not over-brushed. Afirst end of the swing may be as shown in FIG. 7, wherein the centeraxis of brush 32E is aligned to a diameter of wafer 18. The swing range(distance) may be equal to or greater than contact width W1 as shown inFIG. 9 in accordance with some embodiments. The swing range (distance)may also be smaller than contact width W1.

FIG. 8 illustrates a top view of a pencil-type brushing, whereinpencil-type brush 48 is used to further clean wafer 18. Pencil-typebrush 48 may rotate round its axis 50. Pencil-type brushing differs fromthe brushing using brush roller (as shown in FIGS. 2A through 7) in thatin FIGS. 2A through 7, the rotation axes of brushes 32 are parallel tothe surface of wafer 18, while in FIG. 8, the rotation axis of brush 48is perpendicular to the surface of wafer 18. In addition, pencil-typebrush 48 may swing between, and cover, the center and the edge of wafer18, wherein the swing range is illustrated as double headed arrow 44.Accordingly, the wafer center region 18CR, which is not brushed inaccordance with some embodiments, may be brushed.

After the post-CMP cleaning step, the wafer is dried, for example, usingisopropanol and nitrogen gas.

The embodiments of the present disclosure have some advantageousfeatures. By redesigning the size and the location of brushes, andmodifying the operation of brushes, the damage/corrosion observed inconventional post-CMP cleaning process may be reduced.

In accordance with some embodiments of the present disclosure, a methodincludes performing a first post-CMP cleaning on a wafer using a firstbrush. The first brush rotates to clean the wafer. The method furtherincludes performing a second post-CMP cleaning on the wafer using asecond brush. The second brush rotates to clean the wafer. The firstpost-CMP cleaning and the second post-CMP cleaning are performedsimultaneously.

In accordance with some embodiments of the present disclosure, a methodincludes performing a post-CMP cleaning on a wafer using a brush. Thebrush rotates to clean the wafer, and a rotation axis of the brush isparallel to a surface of the wafer. When the brush rotates, the firstbrush swings.

In accordance with some embodiments of the present disclosure, anapparatus for performing a cleaning on a wafer includes a chuckconfigured to hold and rotate the wafer, a first brush having a firstaxis parallel to a surface of the wafer, a first driving mechanism forrotating the first brush, a second brush having a second axis parallelto the surface of the wafer, and a second driving mechanism for rotatingthe second brush.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: performing a first postChemical Mechanical Polish (CMP) cleaning on a wafer using a firstbrush, wherein the first brush rotates to clean the wafer; andperforming a second post-CMP cleaning on the wafer using a second brush,wherein the second brush rotates to clean the wafer, and the firstpost-CMP cleaning and the second post-CMP cleaning are performedsimultaneously.
 2. The method of claim 1, wherein the first brush islocated on a first side of a center of the wafer, and the second brushis located on a second side of the center of the wafer, with the secondside being opposite to the first side.
 3. The method of claim 2, whereina first lengthwise direction of the first brush and a second lengthwisedirection of the second brush are both aligned to a diameter of thewafer.
 4. The method of claim 1, wherein during an entirety of the firstpost-CMP cleaning, the first brush has a first end aligned to a centerof the wafer, and an entirety of the wafer is spaced apart from thecenter of the wafer.
 5. The method of claim 1 further comprising, whenthe first brush rotates to clean the wafer, swinging the first brush. 6.The method of claim 5, wherein when the first brush is at an end of aswing range of the swing, an end of the first brush overlaps a center ofthe wafer.
 7. The method of claim 5, wherein during the swinging, anentirety of the first brush remains on a same side of the wafer.
 8. Themethod of claim 5, wherein the first brush swings in a directionparallel to a lengthwise direction of the first brush.
 9. The method ofclaim 5, wherein the first brush swings in a direction perpendicular toa lengthwise direction of the first brush.
 10. A method comprising:performing a first post Chemical Mechanical Polish (CMP) cleaning on awafer using a first brush, wherein the first brush rotates to clean thewafer, and an rotation axis of the first brush is parallel to a surfaceof the wafer; and when the first brush rotates, swinging the firstbrush.
 11. The method of claim 10, wherein the first brush swings in adirection parallel to a lengthwise direction of the first brush.
 12. Themethod of claim 10, wherein when the first brush is at an end of a swingrange of the swinging, an end of the first brush overlaps a center ofthe wafer.
 13. The method of claim 10, wherein during the swinging, anentirety of the first brush remains on a same side of the wafer.
 14. Themethod of claim 10, wherein the first brush swings in a directionperpendicular to a lengthwise direction of the first brush.
 15. Themethod of claim 14, wherein a swing range of the first brush is equal toor greater than a contact width of the first brush and the wafer.
 16. Anapparatus for performing a cleaning on a wafer, the apparatuscomprising: a chuck configured to hold and rotate the wafer; a firstbrush having a first axis parallel to a surface of the wafer; a firstdriving mechanism for rotating the first brush; a second brush having asecond axis parallel to the surface of the wafer; and a second drivingmechanism for rotating the second brush.
 17. The apparatus of claim 16,wherein the first driving mechanism is further configured to swing thefirst brush.
 18. The apparatus of claim 17, wherein the second drivingmechanism is further configured to swing the second brush.
 19. Theapparatus of claim 16, wherein the first driving mechanism is configuredto swing the first brush in a direction parallel to the first axis. 20.The apparatus of claim 0, wherein the first driving mechanism isconfigured to swing the first brush in a direction perpendicular to thefirst axis.